The purpose of this study is to investigate the influence of volitional movement on excitability of ipsilateral as well as contralateral motor cortical neurons controlling homologous and surrounding muscles. Transcallosal and surrounding inhibitions are well known phenomenon to suppress unwanted movements during voluntary action, which is often disturbed in various movement disorders. Transcranial magnetic stimulation (TMS) has been used to investigate these inhibitory mechanisms, but the inhibitory influence during and after voluntary movement has not been well elucidated yet. In normal volunteers, we plan to determine if voluntary movements of one finger influence the cortical excitability responsible for surrounding as well as contralateral homologous muscles, using voluntary movement-triggered TMS. The primary outcome measures would be any changes in motor evoked potential (MEP) size and intracortical inhibition (ICI) parameters.